History lesson

Back when the cities were major freight centers and railroads ruled the freight industry, supplies were brought in to the harbors and handled by private tug/barge companies and the Railroads. Every railroad that served New York City had among its roster of engines and rail cars, a Marine Fleet The marine fleets consisted of tugs, barges, and lighters. 

Freight was moved between railroad and railroad by car floats (barges with mount railroad tracks), railroad and warehouse, warehouse and ship, ship to railroad...you get the idea. Each railroad had it's own barges, they could be open or enclosed, tugs hauling carfloats and barges were everywhere in the harbor.

Today these barges still exist to some extent, some have become parts of marine facility's

  used for storage etc. but for the most part they are either gone or slowly disappearing. Sitting on the bottom along the side of rivers and docks, rotting away.

One of the more interesting items used was the lighter. The lighter was a ship, usually a barge which had a crane on it and was moved around by a tug, 

The lighter was brought alongside a ship out in the harbor and using the crane either loaded or unloaded the cargo with a barge.

Some lighters were steam powered, they were essentially a tug boat with a crane. These were more agile than the tug barge combo, but cost a lot more.

For more on these you can check maritime history or railroad historical sites on the web.